commit 927185c124d62a9a4d35878d7f6d432a166b74e3 upstream.
The kernel uses the OUTPUT_FORMAT linker script command in it's linker scripts. Most of the time, the -m option is passed to the linker with correct architecture, but sometimes (at least for x86_64) the -m option contradicts the OUTPUT_FORMAT directive.
Specifically, arch/x86/boot and arch/x86/realmode/rm produce i386 object files, but are linked with the -m elf_x86_64 linker flag when building for x86_64.
The GNU linker manpage doesn't explicitly state any tie-breakers between -m and OUTPUT_FORMAT. But with BFD and Gold linkers, OUTPUT_FORMAT overrides the emulation value specified with the -m option.
LLVM lld has a different behavior, however. When supplied with contradicting -m and OUTPUT_FORMAT values it fails with the following error message:
ld.lld: error: arch/x86/realmode/rm/header.o is incompatible with elf_x86_64
Therefore, just add the correct -m after the incorrect one (it overrides it), so the linker invocation looks like this:
ld -m elf_x86_64 -z max-page-size=0x200000 -m elf_i386 --emit-relocs -T \ realmode.lds header.o trampoline_64.o stack.o reboot.o -o realmode.elf
This is not a functional change for GNU ld, because (although not explicitly documented) OUTPUT_FORMAT overrides -m EMULATION.
Tested by building x86_64 kernel with GNU gcc/ld toolchain and booting it in QEMU.
[ bp: massage and clarify text. ]
Suggested-by: Dmitry Golovin dima@golovin.in Signed-off-by: George Rimar grimar@accesssoftek.com Signed-off-by: Tri Vo trong@android.com Signed-off-by: Borislav Petkov bp@suse.de Tested-by: Tri Vo trong@android.com Tested-by: Nick Desaulniers ndesaulniers@google.com Cc: "H. Peter Anvin" hpa@zytor.com Cc: Ingo Molnar mingo@redhat.com Cc: Michael Matz matz@suse.de Cc: Thomas Gleixner tglx@linutronix.de Cc: morbo@google.com Cc: ndesaulniers@google.com Cc: ruiu@google.com Cc: x86-ml x86@kernel.org Link: https://lkml.kernel.org/r/20190111201012.71210-1-trong@android.com [nc: Fix conflicts due to lack of commit 58ab5e0c2c40 ("Kbuild: arch: look for generated headers in obtree") in this tree] Signed-off-by: Nathan Chancellor natechancellor@gmail.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/boot/Makefile | 2 +- arch/x86/realmode/rm/Makefile | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile index 6da2cd0897f3..e94745321cac 100644 --- a/arch/x86/boot/Makefile +++ b/arch/x86/boot/Makefile @@ -100,7 +100,7 @@ $(obj)/zoffset.h: $(obj)/compressed/vmlinux FORCE AFLAGS_header.o += -I$(obj) $(obj)/header.o: $(obj)/voffset.h $(obj)/zoffset.h
-LDFLAGS_setup.elf := -T +LDFLAGS_setup.elf := -m elf_i386 -T $(obj)/setup.elf: $(src)/setup.ld $(SETUP_OBJS) FORCE $(call if_changed,ld)
diff --git a/arch/x86/realmode/rm/Makefile b/arch/x86/realmode/rm/Makefile index 2730d775ef9a..228cb16962ba 100644 --- a/arch/x86/realmode/rm/Makefile +++ b/arch/x86/realmode/rm/Makefile @@ -43,7 +43,7 @@ $(obj)/pasyms.h: $(REALMODE_OBJS) FORCE targets += realmode.lds $(obj)/realmode.lds: $(obj)/pasyms.h
-LDFLAGS_realmode.elf := --emit-relocs -T +LDFLAGS_realmode.elf := -m elf_i386 --emit-relocs -T CPPFLAGS_realmode.lds += -P -C -I$(obj)
targets += realmode.elf